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Dangerous! Snapped chain!


#21

The photo in my post is step 6 in the “Sled” section of the Maslow assembly guide. It shows the cotter pin going through the very first link at the end of the drive chain. This is apparently the weakest link, as there is no pin in the end link. The solution is to run the pin through the next link up the chain. This shortens the chain 6.35 mm, and will affect the calibration (probably not in a good way). If your machine is calibrated, we should be able to move the chains over 1 link on the drive cogs towards the sled to compensate for the shortening of the chain, and preserve the calibration. If the machine is not calibrated, I believe the calibration routine will compensate for the slightly shorter chain, but ultimately, the firm and software will need to be updated, which, as you know, is an ongoing process.

Sorry, no photo right now… am away from the machine.


#22

The only thing that might need to be updated is to include a note in GC on the step the chain is attached to the sled (it’s pretty silent on that right now… just says to attach the chains to the sled). But people don’t seem to read the instructions anyway, so not sure it makes much of a difference :slight_smile:


#23

Always it is responsible to put warnings into the instructions. Even if no one reads them, to protect the developers and company from aggressive injury lawyers. They are everywhere.


#24

We were discussing protecting against this in the Fault Detection thread.

Maybe a simple circuit completion sense could be run through the chains to cut the power if the sled disconnects. (Assuming the chain is conductive end-to-end.)


#25

FWIW, it’s very common to specify the working load as 1/10 of what it takes to break it (or the yeild strength if you prefer) to provide a safety factor, don’t know if that’s a convention, “standard”, or legislated. 85# working is 10% of 850…


#26

the chain is conductive, but the triangulation kit may not be.

David Lang


#27

To take the second link should be the advise after seeing this.

A simple additional security feature is a flexible wire between both chains:


In red measured at widest chain angle:

In this imaginary sled the Z back supports are triangles, so ICE the wire would hit the spindle.
Strategically placed catch hooks can solve this.

After seeing a picture of a sled torn into 2 pieces back in the bracket days I had this for a few days :man_facepalming:


Set your 12 o'clock position with a level... because
#28

@marcpbcup at what depth (stepdown) were you cutting when this happened?


#29

I’m cutting a $600 3/4" Cast Acrylic and after seeing what happen I did install couple finishing nails at the end of the chain. I can’t screw this up I don’t have an extra.


#30

Can I be nosy and ask what you are making?


#31

I like your fix (straight forward and simple). I am going to install a set of small bolts (if I can find some) into the holes that should hold the link pins. This should solve the matter, without having to re-calibrate everything.


#32

I’m Making pocket Letters .37"deep in to the acrylic… for a Ballroom Dance Competition, DBDC
The Letters will sit on a base with LED lights that will reflect on the unpolished acrylic.
It should look good.

To give you an idea look at LED EXIT sigh … That is the look that I’m goin for.

Cheers


#33

@bar @blurfl @dlang @mooselake , what would be the max stepdown before having a chain snap? I know there are so many variables; feedrate, material, flute length, etc… would seem like something would give way (motor gear, pcb or chain) if trying to cut through thicker material in one pass.


#34

I’m not much help on that, I’ve never tried for deep cuts. I usually use shallow ones hoping for better accuracy. Accuracy is higher on my list than speed.


#35

Yes, I’ve always set the stepdown as half the diameter of the end mill.


#36

the tensil strength of the chain is ~10x the max force the motors put out. I
would expect the motors to stall and stop moving LONG before the chain is in any
danger.

David Lang


#37

please see the pending edit here -

If you don’t want to back up a link - I’d use JB weld to glue the end together. I still suggest just backing up a link.

Thank you


#38

I’m not sure I would trust JB weld, applied properly it would do the job, but
you have no way of knowing if it got a really good grip on the material until it
comes apart.

David Lang


#39

I’ve suggested the best method, this is a stop gap if not following the best method.

Your milage may very.

Thank you


#40

I like the idea of inserting a small bolt into the last open part of the chain. This would mean there’s no geometry change to a calibrated machine, and no need for any adjustments, though if I understand right the only change is a quick adjustment in ground control to simply shorten the defined chain length?

Another problem with adding a bolt to replace the missing pin is you will likely not clear the gap in the carriage that the chain passes through, making for slower sled removal if/when you need to do that since the bolt needs to come out too. An alternative might be a rivet, which can be hammered flat and should clear the opening in the carriage.